1. Field of the Invention
This invention relates to pneumatic radial tires, and more particularly to an improvement in the prevention of uneven wear produced in low-section pneumatic radial tires to be mounted onto, for example, vehicles running on a good road at a high speed.
2. Related Art Statement
In general, as shown in FIGS. 7 and 8, (tire symmetrical about the circumferential line) low-section pneumatic radial tires 1 having a rib-type tread pattern have a drawback that when the tire is run on a good road at a high speed over a long period of time, uneven wear 6 (shadowed region in FIG. 7) in circumferential direction E or a so-called river wear is produced in a rib 5 defined by main grooves 3 extending in the circumferential direction E of tread 2. This is particularly the case in a outer end portion 5a of an inner rib 5A viewed from the outside edge of the tire.
In these conventional pneumatic radial tires, therefore, there have been proposed various attempts such as a reduction of amplitude in the circumferential rib 5, a change of shape in the main groove 3, arrangement of notch in the outer end portion 5a of the rib 5 and the like in order to solve the above problem. However, all of these attempts do not yet develop the desired effect. Inversely, the reduction of amplitude in the rib 5 brings about the degradation of wet resistant properties in the tire running on a wet road surface. That is, it is very difficult to simultaneously improve the wet performances and the resistance to uneven wear in the pneumatic radial tire.